My iphone is paired with my Sena 50S, and I control it with the jog-dial on the Helmet.
I have all my music selections loaded into my iphone and can hear it clearly through my helmet speakers, even with "ear-peace" earplugs in.
I also have it secondary-paired with my Zumo-XT and it will display what song is being played momentarily at the bottom of the Zumo. I don't play it through the Zumo though.
If I receive a call or text while I'm riding, it will display on my Zumo-XT so then I can decide if I want to address it, or just ignore and keep riding..........
This setup works very well for me, as I can tell with just a momentary visual glance what is happening.